When a computer has been turned on, a multistage starting operation, also called booting, is usually executed before application programs can be executed on the computer. For example, the starting operation on an IBM PC-compatible computer is illustrated below. When the computer has been turned on, a program called BIOS (Basic Input Output System), held in a nonvolatile memory, e.g., EPROM (Erasable Programmable Read Only Memory) or solid-state memory, on the computer's motherboard, is first started. First, the BIOS initializes the screen and the keyboard and tests the memory modules in the computer's volatile memory. Then, settings for important peripheral devices are read from a further nonvolatile memory (usually a battery-buffered CMOS chip). For the rest of the boot operation, the stored information is read concerning connected hard disk drives and other mass memories, such as optical drives. A first data sector, called Master Boot Record (MBR), is then read in from one of the connected drives. The MBR contains information relating to the course of the rest of the starting operation and defines the independent subsections (partitions) of the hard disk drives. In addition, the MBR contains a program, called First Stage Boot Loader, whose task is to search for what are known as boot sectors on the specified partitions of the hard disk drives. A boot sector which has been found contains a further program, called Second Stage Boot Loader, which in the simplest case directly starts an operating system held on this partition. In other cases, for example, the Second Stage Boot Loader provides the user with the opportunity to select between different operating systems held on different partitions. In addition, the Second Stage Boot Loader can be designed to start an operating system which is not held on one of the hard disk drives or on a further mass memory drive but rather is loaded via a network connection, for example, or is held on a plug-on replaceable storage medium, e.g., a USB (Universal Serial Bus) memory or a solid-state memory card.
The known boot process outlined makes it possible to intervene in the boot operation at several points:                BIOS setting for stipulating the Master Boot Record,        contents of the Master Boot Record (First Stage Boot Loader),        contents of the boot sectors of the starting partition (Second Stage Boot Loader).        
These intervention options for the user allow the boot operation to be matched to the user's own needs. However, these intervention options create security problems as a result of it being possible to manipulate settings or the Boot Loader programs. For example, appropriate BIOS settings can load an extraneous operating system from a CD or some other optical storage medium, and can read data, in unauthorized fashion, from this operating system. These BIOS settings are protected against access via password protection, by the operating system, which is actually provided for the computer. For this very reason, the BIOS typically provides the option of permitting booting only from particular mass memories and/or protecting these settings via a password which is stored in the CMOS memory of the BIOS. The protective properties of a method of this kind or similar can usually be bypassed using very simple methods. By way of example, simple manipulation by interrupting the power supply to the CMOS memory on the computer's motherboard by briefly removing the supply battery for the CMOS memory is sufficient to remove the password protection in the BIOS.
It is also usual practice, in the known boot processes, to install an operating system from an installation medium (CD, DVD) provided by the manufacturer in a local version, matched to the configuration of the computer, on a hard disk drive in the computer. This practice also permits a large number of manipulation opportunities, and in this case, not while the operating system is starting, but during its operating phase. For example, many important files used by the operating system, known as “system files”, are available on the hard disk drive, frequently unprotected against access. Application programs which are installed can overwrite these files with their own versions of these system files, matched to their requirements, which means that sometimes correct operation of the system or further applications are no longer guaranteed.
A further drawback of known boot processes in which an operating system is transferred by installation to a nonreplaceable mass storage medium on the computer is that the user's preferred settings and configurations for the operating system must be individually set for each computer the user would like to use.
An exception in this case is installations within a defined network, where the settings can be held centrally on a server and can be loaded from this central server onto the local computer whenever the computer is started. If such a situation is not present, e.g., in the case of computers or mobile computer which are not part of the network, a user is initially confronted by an unfamiliar working environment on every computer used. Sometimes, for example in the case of partially sighted users, an incorrectly set working environment can not only make the use of the respective computer more difficult but can also make it impossible.